1. Field of the Invention
The present invention relates to a motor-assisted bicycle and a power unit therefor, and more particularly to a motor-assisted bicycle and a power unit therefor in which the power unit is after-mounted on an existing bicycle frame without largely changing the design of the bicycle frame so that an assist power generated from the power unit is input into a chain line.
2. Description of Background Art
For widespread use of a motor-assisted bicycle, it is desirable to manufacture a versatile and inexpensive motor-assisted bicycle by after-mounting a power unit and a battery on an existing bicycle frame without largely changing the design of the bicycle frame. For example, Japanese Utility Model Publication No. 48-33175 discloses such a motor-assisted bicycle that a power unit is after-mounted on an existing bicycle frame without largely changing the design of the bicycle frame and that an assist power generated from the power unit is input into a chain line.
In the prior art mentioned above, the bicycle is designed and manufactured so that the power unit is intended to be after-mounted. That is, the power unit to be after-mounted is specific to the bicycle. Thus, no consideration is given to the versatility so that a common power unit can be after-mounted on the bicycle frames of various bicycles without largely changing the design of each bicycle frame.
In the case of inputting the assist power into the chain line, a drive sprocket of the power unit must be located so as to mesh with a chain at any position on the chain line. However, the bicycle frames have various sizes and structures, so that there is a case that the position of inputting the assist power through the drive sprocket into the chain may be limited to the front side of a crankshaft or to the rear side of the crankshaft, depending on the sizes and structures of the bicycle frames. Accordingly, a common power unit cannot be used for the various bicycle frames. As a result, in the case of newly planning a motor-assisted bicycle, a bicycle frame itself of this bicycle must be newly redesigned, causing a low versatility.
In the case of inputting the assist power into the chain line, the drive sprocket of the power unit must be located so as to mesh with a chain at any position on the chain line. Accordingly, a chain cover must be provided so as to cover both the pedal sprocket and the drive sprocket, so that a conventional chain cover cannot be used as it is. However, no consideration is given to a chain cover in the prior art mentioned above.
It is accordingly an object of the present invention to provide a motor-assisted bicycle having a chain cover for functionally covering the drive sprocket of the power unit together with the pedal sprocket and the chain without marring the appearance.
It is accordingly an object of the present invention to provide a motor-assisted bicycle which can be configured by after-mounting a common power unit on an existing bicycle frame without largely changing the design of the bicycle frame regardless of the type of bicycle frame. It is another object of the present invention to provide such a power unit.
In accordance with the present invention, there is provided in a motor-assisted bicycle having a power unit for inputting an assist power into a chain according to a depression force input from a pedal into said chain, the improvement comprising a bicycle frame having a plurality of flanges for fixing said power unit; said power unit having a plurality of boss forming spaces for forming bosses to be fixed to said bicycle frame, said bosses being selectively formed in at least a part of said boss forming spaces; and means for fixedly connecting said bosses of said power unit to said flanges of said bicycle frame, respectively; wherein the positions of said flanges on said bicycle frame and the positions of said boss forming spaces where said bosses are selectively formed are specific according to variations in kind of said bicycle frame.
With this arrangement, the positions of the plural flanges on the bicycle frame are specific according to variations in kind of the bicycle frame, and the positions of the boss forming spaces where the bosses are selectively formed are also specific according to variations in kind of the bicycle frame. Accordingly, the power unit can be mounted at specific positions on the bicycle frame with specific attitudes according to the kinds of the bicycle frame. Thus, the power unit can be commonly used for different kinds of bicycle frames.
In accordance with the present invention, there is provided in a motor-assisted bicycle having a power unit for inputting an assist power into a chain according to a depression force input through a crankshaft into said chain, the improvement comprising a pedal sprocket mounted on said crankshaft and meshing with said chain; a drive sprocket mounted on an output shaft of said power unit and meshing with said chain; and a chain cover for covering said pedal sprocket and at least a part of a stretched portion of said chain; wherein said chain cover is integrally formed with a drive sprocket cover portion for covering said drive sprocket.
With this arrangement, all of the pedal sprocket, the stretched portion of the chain, and the drive sprocket can be covered with the single chain cover. Accordingly, it is possible to provide a motor-assisted bicycle having a chain cover capable of sufficiently exhibiting the function for the motor-assisted bicycle without an increase in the number of parts.
Furthermore, since the drive sprocket cover portion is integral with the chain cover, the overall shape and color of the chain cover including the drive sprocket cover portion can be made uniform, so that the appearance is not marred in spite of the presence of the drive sprocket cover portion.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description